Method of reducing aromatic nitrogen compounds



2,831,893 Patented Apr. 22, 1958 METHOD OF REDUCING AROMATIC NITRGGEN COMPOUNDS Allen Walter Sogn, Wiiliamsville, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application July 14, 1955 Serial No. 522,164

8 Claims. (Cl. 260-4569) and 2,684,358. of a certain class of naphthoquinoid compounds as reduction promoters in the processes of said patents.

compound, naphthoquinone or a quinoid hydroxynaphthalene compound.

The primary object of the vide improved reduction promoters of said type which,

vantages are secured.

Additional objects in part will be obvious and in part will appear hereinafter.

According to the present invention the foregoing objects are accomplished and other benefits are secured by reduction promoters.

The furano-naphthoquinoid compounds employed as reduction promoters in accordance with the present invention are condensed nuclear substitution derivatives of through two jointly They constitute the class thalene nucleus, and which are in quinoid relation to each other, and preferably in para-quinoidrelation to each other, is linked to an oxy substituent and the carbon atoms of another pair of adjacent carbon atoms that form part of said benzene nucleus also form part of a five-membered heterocyclic nucleus which contains, as the sole heterocyclic element, one of the first two elements of group VI of the periodic table, directly linked to one of the latter pair of carbon atoms.

They include (a) Diones (quinones in which oxygen atoms) (b) Diols (leuco-compounds or hydroquinones, in which both oxy substituents are hydroxyl radicals) (c) Addition compounds of such diones, for example with bisulfites or heavy metal salts, such as these disclosed in U. S. P. 2,645,636

(d) Functional derivatives of such diones and diols, for example imides, oximes,semicarbazones, hydrazones and esters, which are saponifiable by caustic alkaliesas well as nuclear which one or more both oxy substituents are ample, halogen, hydroxyl, nitro, amino, alkyl, alkoxy, cyano, mercapto, etc.

Thus, furano-naphthaquinoid compounds useful as reduction promoters in accordance with the present invention include the following, which are named in accordance with The Ring Index, Patterson and Capell (1940), pages 234, 237, 335, 338, 427 and 430:

Dinaphtho 2, 1,2,3 furan-8, l 3-dione Dinaphtho l ,2,2,3 ')furan-7,12-dione Naphtho 2,3-b furan-4,9-dione 2-methyluaphtho(2,3-b)furan-4,9-dione Benzo (b) naphtho (2,3-d) furan-6,1 l-dione 4,9-thiophanthrene-dione Benzo (b) thiophanthrene-6,1 l-dione 8-chlorobenzo (b) thiophanthrene-6,1 l-dione 3 -hydroxybenzo(b)naphtho(2,3-d)furan-6,1l-dione 8, l 3-diacetoxy-dinaphtho(2,1,2',3 furan 3-methoxydinaphtho(2,1,2',3 )furan-8,13-dione Dinaphtho 1 ,2,2',3 )furan-7,12-dione-5-sulfonic acid Dinaphtho (2,3 ,2,3 )furan-5,7,12,l3-tetrone Dinaphtho (2,1,2',3 ')thiophene-8,13 -dione S-chlorodinaphtho (1,2,2',3 ')furan-7,12-diol In the form of the para-quinone (dione) they are represented by the formula carboxyl, sulfo,

wherein X is O or S, R and R are each hydrogen or the same or ditferent substituents (such as, halogen, nitro, amino, alkyl, aryl, alkoxy, etc.), or together form part of a cyclic nucleus, and one or more of the nuclear hydrogen atoms of the molecule are replaced by other atoms or simple radicals (such as, those referred to above).

Furano-naphthoquinoid compounds of the above type can be prepared in various ways, a number of which are known. For example, dinaphtho(2,1,2,3')furan-8,13- dione and dinaphtho(l,2,2,3')furan-7,12-dione can be obtained by reacting 2,3-dichloro-l,4-naphthoquinone with beta-naphthol or alpha-naphthol, as described in Berichte, vol. 80 (1947 Chemical Society, 1952, pages 4699-4700. Thiofuran page 52, and Journal of the compounds of the above type can be obtained by reacting a phthalic anhydride with a suitable thiophene com pound, e. g. thionaphthene, and ring-closing the resulting ortho(thenoyl)benzoic acid, for example as described in D. R. P. 499,745. Hydroxy derivatives of the above furans and thiofurans, such as dinaphtho(2,l,2,3)furan- 8,13-diol and dinaphtho(l,2,2,3)furan-7,12-diol, can be obtained by reducing the corresponding diones with a suitable reducing agent; such as, aqueous alkaline sodium hydrosulfite.

I have discovered that the furano-naphthoquinoid compounds of the above type possess exceptional reductionpromoting activity. Thus, I have found that the inclusion of merely a small amount of a furano-naphthoquinoid compound such as dinaphtho(2,l,2',3')furan-8,l3-dione, having the formula or dinaphtho(1,2,2,3)furan-7,12 dione, having the formula \o/ ll 0 in the reaction mixture in which nitrobenzene is subjected to the reducing action of sodium methylate not only promotes the reduction but produces a greatly increased promoting effect and as a direct product of the reduction.

This result is surprising since the use of such small amounts of reduction promoters like 1,4-naphthoquinone and 2,3-dichloro-1,4-naphthoquinone ordinarily does-not produce large quantities of hydrazobenzene as a direct product of the reduction.

In the practice of the'present'invention, the reducible aromatic nitrogen compound is subjected to the reducing action of a metal alcoholate reducing agent in a reaction mixture in which referred to above have been incorporated. In the preferred practice of the invention, wherein the reducible aromatic nitrogen compound is heated with a caustic alkali and an alcohol (preferably sodium hydroxide and methanol) at the boiling point of the reaction mixture,

the reduction promoter is preferably mixed with the alcohol and, after adding the caustic alkali and heating, the nitrogen compound to be reduced is added to the heated mixture. The reduction promoter may be added to the reaction mixture in various ways and at various times, however, without departing from the scope of the invention.

The process is carried out in detail in the manner disclosed in my U. S. Patents 2,645,636 and 2,684,358 referred to above. In view, ing activity of the fur'ano-naphthoquinoid compounds employed as promoters in accordance with the present invention, lesser amounts of reduction promoter than tho'se employed in said patents may be used in the practice of the present invention to secure the same effect, and the minimum effective concentration of the promoter is lower. Furthermore, in view of the greater reduction promoting activity of the furano-naphthoquinoid compounds of the above type, it is possible to obtain reduction products of a lower stage of oxidation leads to high yields of hydrazobenzene i one or more of the promoters however, of the high promot- 4 as the direct product of the reduction by employing amounts of such furano naphthoquinoid reduction promoters similar to the amounts of the promoters employed in the said patents, or it is possible to effect a reduction to a particular stage of oxidation with a decreased amount of the metal alcoholate employed for the reduction.

The invention will be illustrated by the following specific examples, but it is to be understood that it is not limited to the details thereof and that changes may be made without departing from the scope of the invention. The temperatures are in degrees centigrade and the parts are by weight, unless designated as parts by volume in which case the amount signifies the volume occupied by the same number of parts by weight of water at 4 C.

Example 1 Part 1.-Forty-three parts of methanol and one part of dinaphtho(2,1,2',3')furan-8,13-dione were charged to a flask equipped with a reflux condenser, agitator, dropping funnel and thermometer. Then 56 parts of solid sodium hydroxide were added with cooling, and the 'resulting mixture was heated to refluxing. Nitrobenzene parts) was then introduced during about a half hour while maintaining the mass at and the reaction mass was boiled for an additional period of about 21 /2 hours under reflux at atmospheric pressure (about 90 to The mixture was then diluted with water to 3000 parts by volume, cooled to about 10 and filtered, and the filter cake was dried by standing in the atmosphere at room temp erature-253 0 The yield of reduction products cent of theoretical yield based charged, was

thus obtained, in peron the nitrobenzene Percent Hydrazobenzene 72 Azobenzene 27 Azoxybenzene O Aniline 1 Part 2.-When the process of Part 1 was repeated, using one part of 1,4-naphthoquinone in place of the dinaphthofuran-dione, a much smaller .yield of hydrazobenzene was obtained, viz:

Percent Hydrazobenzene 18.5 Azobenzene 80.6 Azoxybenzene --e 0 Aniline 1 Example 2 Percent Hydrazobenzene 48 Azobenzene '51 Azoxybenzene 0 Aniline 1 As noted above, the invention is not limited to the details of the foregoing illustrative examples, and changes can be made without departing from the'scope of the invention.

Thus, the process is applicable to the'reduction of other aromatic nitrogen compounds containing nitrogen in a reducible form as a substituent in a benzene nucleus, as for example, o-nitrotoluene, m-nitrotoluene, 'o-nitr'ochlorobenzene, rn-nitrochlorobenz'ene, p-nitrophe'netole, pnitrobenzoic acid, o-nitrobenzene sulfonic acid, and their reduction products. In'view of the extensive use of 'hydrazobenzene and its o-substituted derivatives (such as o, o'-dichlorohydrazobenzene, o, o-hydrazotoluene, 0,0- hydrazoanisole, o, o' diethoxy-hydrazobenzene, etc.)" as intermediates for the manufacture of benzidine'and're- .reaction mixture, and then to strus" lated derivatives of benzidine, the process of the present invention is of special value as a means for reducing the cost of manufacturing such hydrazo compounds from the corresponding reducible aromatic nitrogen compounds (such as, nitrobenzene and its o-substituted derivatives and reduction products thereof) in which the nitrogen is at a higher stage of oxidation than the hydrazo stage.

Instead of the dinaphthofurandiones employed in the above specific examples, an equal amount of any of the other furano-naphthoquinoid compounds mentioned above may be substituted as reduction promoters.

In carrying out the reduction by means of sodium hydroxide and methanol, it is preferable to employ these reagents in amounts in excess of those theoretically required. Extra methanol over that theoretically required is generally desirable for use as a solvent, and an additional excess is desirable to counteract the diluting effect of the Water formed in the process, which would otherwise tend to retard the reaction. An excess of sodium hydroxide also is desirable since it tends to increase the rate of reaction.

It is possible to carry the reduction of a particular reducible aromatic nitrogen compound to various stages, depending upon the amounts of sodium hydroxide and methanol employed, as Well as the specific nature and amount of the particular reduction promoter employed.

Thus, as illustrated in the above specific examples, it is possible to reduce nitrobenzene to hydrazobenzene in a single reaction mixture. However, it is possible to re duce nitrobenzene to azoxyand/or azobenzene in one isolate and reduce the re sulting azoxybenzene and/or azobenzene to hydrazobenzene with a fresh charge of sodium hydroxide and methanol, if desired.

The temperature at which the reaction is carried out also may be varied although, in the reduction performed with the aid of alcoholic caustic alkali, temperatures at or near the boiling point of the reaction mixture at atmospheric pressure (ordinarily about 90 to 105) are preferred. At lower temperatures, the reaction is slower, under otherwise similar conditions, and may require an excessively long time to produce the same results as the preferred temperatures. Conversely higher reaction temperatures result in a short time cycle but require the use of closed reaction vessels. However, temperatures greatly exceeding 110, though not precluded, are less desirable; since even in the presence of the reduction promoters they lead to evolution of considerable amounts of hydrogen gas and formation of primary amines, with consequent loss of yield of the desired reduction products.

While for economical and simple operation it is preferred to use, as a solvent or diluent of the reaction mixture, an excess of the alcohol employed for the alcoholate, the invention is not limited thereto. Thus, other solvents and diluents can be employed; for example, the process may be carried out with amounts of sodium hydroxide and methanol only slightly in excess over the amounts theoretically required for the reduction, in a reaction medium containing a suflicient amount of xylene or other inert solvent or diluent (such as benzene, toluene, monoand dichloro-benzenes) to provide a stirrable reaction mass. Further, while it is simpler to employ as the solvent or diluent an excess of the alcohol functioning as a reducing agent, other alcohols can be employed; also mixtures of alcohols can be used, especially where it is desired to modify the boiling temperature of the reaction mixture.

As a matter of convenience and for economical operation, the process is generally carried out by forming a metal alcoholate in the reaction mixture; for example, by reacting caustic alkali with the alcohol. If desired, however, preformed metal alcoholates may be employed as reducing agents, thereby avoiding the diluting etfect of 6 the water formed as a tic alkali with the alcohol.

Sodium hydroxide and methanol are employed in the specific examples in view of their relatively lower cost and ready availability. The invention is: not limited thereto, however, and other alkalis (for example, potassium hydroxide) and other alcohols (for example, ethyl alcohol and the various propyl, butyl and higher alcohols) may be employed, if desired.

The products of the reduction can be isolated from the reaction mixtures in any suitable manner. Aside from those cases in which the reaction mixture contains an insoluble residue resulting from the presence of the reduction promoter in the reaction mixture, the isolation of the reduction products can be carried out in the usual manner. Thus, for example, be cooled to crystallize the reduction product and filtered, and the cake washed with water to remove alcohol, sodium formate formed as a by-product of the reduction, and sodium hydroxide. If desired, the reaction mixture to remove the methanol (and by fractional distillation for reuse in subsequent reactions), and the remaining hot aqueous mass can then small amount of insoluble by-product, it may be removed by filtering the hot mixture prior or in any other suitable manner.

This application is a continuation-inpart of my copending applications Serial Nos. 448,376 and 448,377, filed August 6, 1954.

I claim:

1. The improvement in the method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a nuclear substituent of at a higher stage of oxidation than the hydrazo stage by metal alcoholate, which comprises carrying out the reduction in a reaction mixture in which a furano-naphthoquinoid compound has been incorporated, said furano-naphthoquinoid compound being selected from the group consisting of compounds represented by the following formulas:

to the phase-separation,

o R Y R! X H O by-product of the reaction of cansthe reaction mixture may and wherein R and R are each selected from the group consisting of hydrogen and methyl,

is an aryl radical, which is condensed with the furano radical represented by and chlorine-whereby the reduction of the aromatic nitrogen compound is promoted.

2. A method as defined in claim 1, wherein the alcoholate is sodium methylate and the furano-naphthoquinoid compound is a dinaphthafurandione.

3. A method as defined in claim 2, wherein the furanonaphthoquinoid compound is dinaphtho(2,1,2',3')furan- 8,13-dione.

4. A method as defined in claim 2, wherein the furanonaphthoquinoid compound is dinaphtho(1,2,2',3)furan- 7,12-dione.

5. The improvement in the method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a nuclear substituent of a benzene nucleus at a higher stage of oxidation than the hydrazo stage by the action of a metal alcoholate, which comprises heating the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and methanol in a reaction mixture containing a small amount of a furano-naphthoquinoid compound defined in claim 1.

6. A method as defined in claim 5, wherein the furanonaphthoquinoid compound is a dinaphthofurandione.

7. A method as defined in claim 6, wherein the dinaphthofurandione is dinaphtho(2,1,2',3')furan-8,13- dione.

8. A method as defined in claim 6, wherein the dinaphthofurandione is dinaphtho(1,2,2,3)furan-7,12-dione.

References Cited in the file of this patent UNITED STATES PATENTS 2,645,636 Sogn July 14, 1953 

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGEN COMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS A NUCLEAR SUBSTITUENT OF A BENZENE NUCLEUS AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BY THE ACTION OR A METAL ALCOHOLATE, WHICH COMPRISES CARRYING OUT THE REDUCTIJON IN A REACTION MIXTURE IN WHICH A FURANO-NAPHTHOQUINOID COMPOUND HAS BEEB INCORPORATED, FROM THE GROUP CONSISTING OF COMPOUNDS REPRESENTS BY THE FOLLOWING FORMULAS: 